Process for applying alpha protective coating to metallic articles



Patented Oct. 31, 1933 PROCESS FOR APPLYING A PROTECTIVE COATING '10METALLIC ARTICLES Heinrich Klas, Dusseldorf, Germany, assignor to thefirm Vereinigte Stahlwerke Aktiengesellschaft, Dusseldorf, Germany NoDrawing. Application March 27, 1931, Serial No. 525,875, and in GermanyMay 3, 1930 4 Claims. (CI. 91-70) This invention relates to a processfor applying a protective coating to metallic articles.

It is known to dissolve induratable artificial resins in solvents andapply them to articles of 5 various kinds by brushing, spraying ordipping,

and that a suitable filler, such as aluminium powder, finely pulverizedheavy spar or the like, may also be incorporated with the solution. Thehardening of the dissolved resin after the application of the coating,is effected by first raising, or maintaining, the temperature so as tocause the complete evaporation of the solvent, and then increasing thetemperature so as to eifect the partial or complete hardening of theartificial resm. I

This current process is attended with considerable difiiculties, due, inpart, to the nature of the solvent itself, and partly to the method ofproducing such an induratable coating. The evaporation of the solvent(usually alcohol) requires a certain time, and it is not untilevaporation is complete that an elevated hardening temperature can beemployed. Consequently, the complete application process takes someconsiderable time. A further difficulty consists in that, in the firstplace, a temperature suitable for evaporating the solution must bemaintained for a certain period, of at least half an hour, after whichthe still higher optimum hardening temperature must be maintained for acertain minimum period. This process is cumbrous and requires extensiveappliances and control apparatus, together with first-class skilledoperatives. A further difliculty resides in the infiammability of theusual solvents, which must only be used withspecial precautions whichincrease the expense of the operation. Extensive experiments with a viewto improving the various artificialresin coatings and simplifying theprocess of applying same, have also shown that, when ap plied bythe.known process, the elasticity of the artificial resins, undermechanical stresses, such as shock and impact, leaves much to bedesired.

It has now beenascertained that the process of applying a coating ofinduratable artificial resin to metallic articles is substantiallylmproved by dissolving induratable artificial resins in tar oil, with orwithout finely powdered fillers. The employment of tar oil possesses theparticular advantage-in addition to those hereinafter set forththat itsviscosity renders it highly suitable as a suspension vehicle.

Since it is of advantage to employ inorganic fillers which resistchemical action, on the one hand, and possess sufiicient physicalhardness on the other-such as heavy spar, quartzite or otherminerals-suspensions should always be employed when such fillers areused, since the latter are insoluble in the tar oil. The compositionsprepared by dissolving induratable artificial resins in tar oil, with orwithout additions, are applied by brushing, spraying, or by dipping theheated article in the composition.

Additional fillers may consist of organic substances of high boilingpoint, such as anthracene oils, since, owing to their high boilingpointabove 300 C.-they do not vaporize completely during the applicationprocess, but are still present in the hardened final coating, and actfavorably by increasing its elasticity.

Another advantage of employing tar oils consists in that the flash pointis so high as to preclude risk in the performance of the process. Sincethe boiling points of tar oil range between about 180 and 360 C., whilstthe hardening temperatures of the artificial resins lie between about 80and 300 C., it is possible to select tar oils which boil within a rangeapproximating to the temperature limits within which the hardening ofthe artificial resins proceeds with the requisite velocity. In thismanner it is possibha not only to prevent the formation of bubbles,which is a source of considerable difiiculties in other methods ofapplication, but also to avoid treatment at difierent temperatures, suchas inevitable in the case of other solvents. In the case of theselatter, it is first necessary to employ a low temperature in order toevaporate the solvent, and only thereafter to proceed to the higher,actual hardening temperature. Operating in this manner necessitateseither employing two stoves, together with the devices for transferringthe articles from the one to the other, or else the gradual heating ofthe coated articles up to the hardening temperature. The consumption ofmaterial, heat and time thereby entailed is obviated by thehereindescribed process. In this case, the temperature of the tube maybe approxi-v mately the same, during the application oi 'the artificialresin and tar oil compositions, as'that required for the hardeningstage, provided merely that the optimum hardening temperature be bornein mind when selecting the tar oil to be employed, or conversely that,in the case of tar oils with a given range of boiling points, thehardening temperatures of the resins employed approximately coincidewith said range of boiling points.

The previously mentioned beneficial action of a content 01' organicsubstances of high boiling point, such as anthracene oil (b. p. above300 C.) in the finished, hardened coating, can be easily obtained inaccordance with the invention, by adding a certain amount of anthraceneoil, boiling above 300 C., to the tar oil employed as the solvent. Thecoatings obtained in accordance with the above described principles aredistinguished by extreme compactness and adhesion, and thus areunusually resistant to chemical and mechanical influences.

Example A tube of any convenient metal or metallic alloy, which haseither been previously heated in a'suitable and known manner, or isheated to about 260-280 C. during the operation, is brushed or,preferably, sprayed with a mixture prepared, in known manner,bytriturating tar oil (b. p. 210-240 C.) with a mixture of finelypowdered artificial resin and finely powdered quartzite in equalproportions. If necessary, a short supplementary hardening of thecoating may be performed at a suitable temperature. The coating may beapplied both outside and inside.

I claim:-

1. A process for applying a protective coating to metallic articles,which comprises applying a composition containing a solution ofinduratable artificial resins in tar oil and an organic substance suchas anthracene boiling above 300 C., to a metallic article whilstheating.

2. A process for applying a protective coating to metallic articles,which comprises heating the metallic article and then applying acomposition containing a solution of induratable artificial resins intar oil and an organic substance such as anthracene boiling above 300 C.to said metallic article.

3. A process for applying a protective coating to metallic articles,which comprises applying a composition containing a solution ofinduratable artificial resins in tar oils having a range o1 boilingpoints approximately corresponding to the temperature at which thetransformation of the artificial resin into the insoluble and infusibleform proceeds at suitable velocity and an organic substance such asanthracene boiling above 300 C., to a metallic article whilst heating.

4. A process for applying a protective coating to metallic articles,which comprises heating the metallic article and then applying acomposition containing a solution of induratable artificial resins intar oils having a range of boiling points approximately corresponding tothe temperature at which the transformation of the artificial resin iniothe insoluble and infusible form proceeds at suitable velocity and anorganic substance such as anthracene boiling above 300 C. to saidmetallic article.

HEINRICH KLAS.

